<!DOCTYPE html>
<html>
	<head>
		<meta charset="utf-8">
		<title></title>
	</head>
	<body>
		<script>
			var arr = ["a","b","c","d","c","b","a"];
			
			console.log(arr.indexOf("a"));
			console.log(arr.indexOf("b"));
			console.log(arr.indexOf("x"));
			
			console.log(arr.lastIndexOf("a"));
			console.log(arr.lastIndexOf("b"));
			console.log(arr.lastIndexOf("x"));
		</script>
	</body>
</html>
